In the United States, ______ farms feed 200 million Americans plus the equivalent of another 160 million people around the world, the agriculture population is below 6 percent and it is still shrinking rapidly.
 
【正确答案】 A
【答案解析】 这是whose引导的定语从句。当先行词与从句中某个名词有所属关系，表达“……的”意思时，用关系代词whose 引导定语从句，它既可以指代人，也可以指代物。在本句中则表示“美国的农场”。whose引导定语从句时,通常可与of which/of whom引导的定语从句进行转换。